Generally a packaged semiconductor device includes a semiconductor die attached to a copper lead frame plated with other metals, such as nickel or silver. The die is then connected to leads by bonding wires made from, generally, aluminum, gold, or copper to a wire bond site on the die and bonded on its second end to a corresponding lead. For example, an aluminum wire on its first end is bonded to a source contact on the die and its second end is bonded to a source lead. Thereafter the device is packaged leaving the leads exposed through the packaging material to connect the packaged semiconductor device to an electronic device in which it is placed.
Since copper is a relatively cheap metal, lead frames are generally made at the basic level of copper and then plated with other materials such as nickel or palladium, or even both. Nickel and palladium are known to have a reliable intermetallic connection with aluminum. Silver is also used to plate copper lead frames because this metal, too, has a reliable intermetallic connection with gold. However, Aluminum and copper, for instance, are not known to have a reliable connection. Aluminum and copper create several intermetallic phases that are brittle and that lower shear strength at certain temperatures which increase the growth of brittle copper-aluminum intermetallic phases, and thereby cause breakage in the wire or bond.
Aluminum and nickel, for instance, are a reliable metallurgic system because it is not susceptible to Kirkendall voiding or galvanic corrosion. Further, nickel and copper are resistant to sulfuric and hydrofluoric acids. Thus, it is desired in the art to produce a cost competitive product. Further, it is desired to produce a product using metals more efficiently to reduce costs while still manufacturing a device with reliable metallurgic systems.